This invention relates to an automatic air inlet system, such as a choke, for an internal combustion engine. More particularly, this invention relates to an inlet control system that is responsive to an engine air flow.
It is known to use a manually-operable starting device to assist in starting of a small internal combustion engine. Typical manual starting devices include a primer or a choke, which may be used together in some applications. A primer typically provides a charge of fuel before the engine is started to assist in starting, particularly at lower temperatures. A choke valve is typically positioned in the air intake passageway, and reduces the amount of intake air to thereby enrichen the air/fuel mixture during engine starting.
A major disadvantage of such prior art starting devices is that they must be manually operated by the user in the correct manner for them to be effective. With a manual choke, for example, the operator must typically move a choke lever into the appropriate choke position, start the engine, and then quickly move the choke lever to the disengaged position. The choke lever must be moved to the disengaged position once the engine has started to prevent the engine from stumbling or stalling.
Automatic chokes are known for use with internal combustion engines. Such chokes are typically microprocessor-controlled, are complicated and are expensive. The expense of such microprocessor-controlled automatic chokes will typically make such chokes impractical for use on a small, relatively inexpensive internal combustion engine.
There are several problems in attempting to design an inexpensive automatic choke for an engine. One problem is that the choke must automatically disengage at an appropriate point to keep the engine from stumbling or stalling after it has started. A second problem is that the choke should be disengaged during hot restarts of the engine, while at the same time being automatically engaged during starting of a cold engine. It is desirable to disengage the choke during hot restarts to prevent stumbling or stalling of the engine when the engine is already warmed up, and to reduce the amount of unburnt fuel and noxious exhaust emissions during hot restarts.
An automatic choke is known that is operable using the air flow from an air vane. In U.S. Pat. Nos. 3,863,614 issued Feb. 4, 1975 and 4,031,872 issued Jun. 28, 1977, an automatic choke is disclosed that uses an air vane, and has two oppositely-wound bimetallic coils to control the influence of the air vane. One of the coils keeps the choke open during hot restarts of the engine. However, this apparatus is complicated and expensive, and may not be feasible for a small, relatively inexpensive internal combustion engine. An automatic choke using an air vane is also disclosed in U.S. Pat. No. 5,503,125. It has a two spring linkage which controls the air vane at no load and light load conditions. However, the device provides no structure to keep the vane open for hot restarts.